Tm3+ and Ho3+ colasing in in-band pumped waveguides fabricated by femtosecond laser writing

Abstract

We report on the first, to the best of our knowledge, in-band pumped Tm³⁺,Ho³⁺ codoped waveguide (WG) laser. A depressed-index surface channel WG (type III) with a 50 µm half-ring cladding is fabricated in a 5 at. % Tm³⁺, 0.5 at. % Ho³⁺:KLu(WO₄)₂ crystal by femtosecond pulse direct laser writing. Under in-band pumping by a 1679 nm Er Raman fiber laser, Tm³⁺ and Ho³⁺ colasing is observed in the WG and explained by bidirectional energy transfer. The maximum total output power at ∼1942nm(Tm³⁺) and 2059 nm (Ho³⁺) is 448 mW with a slope efficiencyM of 40.6%, which is a record high for this type of WG lasers. The maximum output power of the Ho laser reaches 144 mW.